Abstract
Solution process is the most widely used method to prepare perovskite films for efficient solar cells due to its facile fabrication and low-cost. However, the aged perovskite precursor solutions usually suffer from degradation, which impedes the reproducibility of the solution. In this paper, we demonstrate the direct formed tri-iodide ions stabilizing colloidal precursor solution for efficient halide perovskite solar cells. The added I2 molecules dissolved in perovskite precursor sustain the dynamic balance between I− ions and I3− ions by the reversible reaction: I− + I2 ⇌ I3−, which effectively stabilizes the whole I− ion concentration in perovskite solution and prevents the colloidal particles from aggregation. The resulting perovskite films with better crystallization have less bulk defects that act as carrier recombination centers. As a result, the devices using the aged solution with the additional tri-iodide ions show the less efficiency drop from ∼19% to ∼16% with the increased aging time up to 15 days, compared with the devices using the as-prepared precursor solution degrading from ∼18% to ∼6%. Our results represent an important advance in the stabilization of perovskite colloidal precursor and promote the reproducibility of perovskite solar cells by solution process.
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